Aspergillus niger, a type of black mold, "could probably be found on every table-top in the world," says Richard Summerbell, research director of biotech Sporometrics in Toronto. It can cause everything from black fuzz on onion bulbs, to toenail infections, to painful and itchy swelling and discharge from the ears of children who stick dirty toys inside.

But A. niger, Summerbell points out, is also a workhorse of industry. For example, it can turn sugars into citric acid, the white powder that's ubiquitous in foods, beverages, detergents, cosmetics, and pharmaceuticals. The fungus can also produce useful enzymes, such as alpha-galactosidase, the main ingredient in the anti-flatulence pill Beano.